effects of map switch on engine?

[swazi_matt]

I was asked recently if there are any adverse effects on the engine when running in one of the different map modes.

ie if running in rain mode does it pre ignite the engine? will the bike not run hotter at higher revs (is it safe to leave it in rain mode)? Does it affect jetting and fuel consumption?

 

[dank]

this is just observation, but from what i have seen, the switch only changes ignition by a little bit, and will not damage the engine. i doubt companies would make a changeable ignition if there was a distinct possibility of damaging the engine anyhow.

 

[GMP]

The advance curve for a two stroke is not like a four stroke, crude by comparison. Some guys including myself have poked around with a timing light, and also found information to support the finds. Basically the timing goes to full advance at a low to mid RPM, stays there for most of the RPM band, and the rolls off a bit on top. From what I can tell, the switch simply changes the RPM at which the system goes to full advance. More advance equals more low end torque, If this is lower it will pull harder through the range onto the pipe, if higher RPM it will be initially softer. This is only a few degrees and like was said many times is not a big difference. I suppose if your jetted on the very edge of lean in rain mode, or your static timing(stator position) is advanced more and go to sun it could ping, but I have never had a problem and mine is crisp. Its possible that the high RPM roll off is different but I don't know, as far as I wanted to rev the bike on the stand the timing looked constant.

 

[blitz11]

I'll have a full report on ignition timing and Kukosan 2k-2 or 2k-3 which is on my bike (2002 EC 300). I have my prototype ignition working, and am in the process of building a test rig / automated test to test different CDI boxes. Right now, my test bench is my lathe, and i can only spin to 7K RPM. At around 6500 RPM with my ignition, i see the retarding of the advance.

A generic curve looks like this:

RPM Advance
0-2000 17 deg
3500 27 deg
9000 17 deg
10000 9 deg
12000 7 deg

Again, the above is NOT our bikes, just a generic curve. The kukosan looks a bit less crude than that above.

I am getting my a$$ kicked at work (again). My plan was to have a report before the holidays, but it looks like that won't happen until after. It is all pretty interesting.


Once i build the test rig, i might be able to test individual CDIs to see how the map affects timing, etc. I also may try to beg some free dyno-time so i can map out the effects of ignition timing on power delivery, jetting, etc. We'll have to see about the latter.

I may be asking for donor CDIs to test if people are interested. It just snowed 17" this weekend, so I have nothing better to do.

blitz.

 

[GMP]

Nice! Did you do a DC-DC converter to charge the cap or use the stator winding? If DC-DC could/did you up the cap size to incease spark energy? Very cool, good luck and keep me posted.

 

[blitz11]

I should clarify: working, not perfected. I can spark on the bench, but what I have needs work before it goes into the bike.

The big issue (as always) is the power supply. I am looking at different power supply topologies. Kukosan uses a very low voltage AC to power their CDI. This provides some "opportunities" to design a sly power supply. My old XR250 used much higher AC voltage from the alternator. That made for a more expensive alternator, but simplified CDI design. Kukosan saves money with a less powerful alternator. That's why the CDI for my xr is $50.

(BTW, the lighting circuit on my bike sucks. hardly any voltage generated there. you have to spin the crap out of it to generate any voltage at all. No wonder the lights suck.)

On the other hand, Kukosan uses a very low voltage alternator, then steps it up in the box. At 600 RPM, they generate 20VAC at the alternator, yet the CDI delivers 120 Volts to the coil at that speed. The tricky bit is to get that voltage at low speed, but not have KV at 10,000 RPM and still make this inexpensive and more reliable than theirs. OK, inexpensive.

I think I had a bad coil on my bike (which motivated this). It's been flawless on the bench with a new coil, but not with the old coil. (I have an alternative coil which cost $11 instead of the $135 Kukosan unit, and it seems to work really well).

The timing/advance stuff is pretty straightforward. The magic is the power supply. The fun is that there are so many ways to skin this cat.

So, I'll keep working on the power supply, and report when i have something cool (and time to document it).

blitz.

 

[blitz11]

Oh, Cap Sizes.

Bigger isn't necessarily better. If you use too big of a cap, you can't charge it completely at high speeds. Since E - 1/2CV^2, you lose spark energy with too large of a capacitor 'cause you don't have time to fully charge it. If you don't regulate the cap voltage, you end up with a cap with 1kV across it. You don't want that. (Ahh, power supplies.)

What really matters in terms of the spark is the voltage at which you charge the cap. You can multi-fire the cap (i am using 2uF at 400V, which is overkill) at least twice (i forget now how close together you can). I haven't tried more than 2 sparks per stroke-cycle.

blitz

 

[GMP]

Yes, the power supply. I was thinking of starting with something similar to the example in the Sportsdevices link, a small switchmode ckt based on the Maxim chip. For LV DC input what do you think about just using the lighting coil output with a 12V rect/reg. This could charge a small battery, or just use a cap, and the stator winding output in conjunction for starting before the DC-Dc can run.

Yeah, I can see how you could run out of time to charge a big cap at high RPM but if your supply is stout enough this should not be a problem. I once worked on an NdYag surgical laser, which electronically is basically a VERY powerful strobe light to lase the crystal and associated power supply(s). There were two HV ckts/caps that charged at offset times to enable higher pulse rates.

I guess the correct way to approach it would be to determine what the point of dimminishing return is in terms of spark energy (or the ability to create multiple sparks), and pick a cap size / power supply. That would mean dyno time though.

About the coil, I beleive I fixed my problem as well and will post in the other thread.

Blitz, good luck and have fun, I wish I had the time to play with this.

 

[Leo]

Sun/Rain mode comparison movie
http://youtu.be/XkJQsVgMTLE